Recently, I have been helping to edit and clean up the Wikipedia project. I have been consistently surprised at the quality of information already present, and I rarely can find anything useful to add to the major articles. This is to say that I think the Wikipedia project, although clearly fallible, is often accurate and precise.
In contrast, I present for your approval this article about vacuum furnaces. Now, it is on the “international journal of thermal technology” website, by the “heat treat doctor” who even cites his sources. You don’t have to read the entire article to get to the good part, I’ll copy the important paragraph (in its entirety)
Now for a surprise and an important concept. At atmospheric pressure, one cubic centimeter of air contains approximately 2.69 x 1019 molecules all moving around in a random motion. As you might expect, this results in a fantastic number of collisions. In other words, the mean free path between molecules (or the average distance a molecule can travel before colliding with another molecule) is only about 2.6 x 10-6 inches. So if we pump a one-cubic-centimeter volume down to a micron (1 x 10-3 torr), which is a vacuum level commonly used in heat treating, we still have about 3.54 x 1013 molecules, or well over half of them remaining! You might be wondering how this can be an acceptable condition for heat treating, especially when about 20% of those remaining molecules are oxygen? The answer is that the mean free path increases dramatically, reducing the probability of molecular collision with the surface of the workpiece.
First, give him the benefit of the doubt that when he says 1019 he means 10^19, likewise with 1013 meaning 10^13. If not, then he just needs to ask a highschooler what Avogadro’s number is. Okay, now someone tell me how a reduction of about 1,000,000 (yes, that’s one million) times can still leave “well over half” of the molecules? I’m still sitting here in astounded wonderment! That he goes on to spout about how “mean free path” is the reason heat treated surfaces don’t oxidize in the furnace shows that he really has no clue what he is talking about. To make matters worse, this was linked from the “Coatings and surface engineering” newsletter on GlobalSpec, a major engineering resource site. Did no one read what this guy is saying? The link from GlobalSpec says he “explains some of the basics” of what a vacuum is. This is the main point of his article! Did no one notice that he can’t read scientific notation, and compensates by making stuff up?
That people make mistakes is no surprise. What riles me is I could probably get away with citing this article in any engineering class, but if I cited Wikipedia I’d suddenly be on unfounded ground. The academics seem to have a penchant for the immutable, even if it is immutably wrong. Now, to be fair, I’ve just pitted a single errant example by a single man against an army of dedicated Wikipedians. On the other hand, if this article was on Wikipedia, I would have corrected it by now.